The present invention pertains to a gas chromatograph detector (GCD) for selective detection of compounds which have photo-responsive properties in their gas phase. More particularly the instant invention pertains to a detection chamber through which a compound in a gaseous-phase passes, wherein it is bombarded with light that causes the gas to fluoresce. Fluorescent properties of the gas are measured by light sensing devices adjacent to, and remote from, the detection chamber. The fluorescence producing light is generated at a site remote from the detection chamber.
Gas chromatography is used to separate organic compounds in a solution. A solution is vaporized and then passed through a chromatographic column, where the individual compounds are separated. One technique of identifying such separated compounds is through the use of a flame photometric detector (FPD), which ignites the subject gas after it has passed through a chromatographic column. The FPD destroys the compound in the analysis process. Ultraviolet or visible light absorption is also used to detect certain compounds.
A further method of detecting photo-responsive compounds is to dissolve gaseous effluents in a liquid solvent, and analyze the resultant solution fluorescence with traditional flow-through spectrofluorometric techniques.
Another method is the interface of a conventional spectrofluorometer to a gas chromatograph. The use of a spectrofluorometer, while providing information about compounds present, is an expensive technique which require the use of a machine which costs in excess of 20,000., and requires the use of heated transfer lines between the chromatograph and spectrofluorometer.
Rapid scanning instruments and flow-through cells, with heated transfer lines, have been used to effect low nanogram limits of detection of selected compounds. Silicon intensifier targets and laser excitation have also been used to detect low levels of aromatic hydrocarbons in their gas-phase.
For a variety of reasons, the above methods of detection are more suited to research laboratory practices than they are to real world use to detect the presence and quantity of photo-responsive compounds.
Of particular interest are groups of compounds with fluorescent photo responsive properties known as polynuclear aromatic compounds (PNA's). These compounds include many toxic chemicals as well as known carcinogens.
An object of the instant invention is to provide a detector which will detect sub-nanogram amounts of compounds which have photo-responsive properties in their gas-phase.
A further object of the instant invention is to provide a detector which will not require the use of heated transfer lines between a gas chromatograph and detector chamber.
A further object of the instant invention is to provide a gas chromatographic detector which will measure the fluorescent emission of compound in its gas phase through excitation by a light source.
Yet another object of the instant invention is to provide a detector which will measure light absorbance by a compound in its gas phase.
A preferred embodiment of the instant invention includes a gas chromatographic column, which is enclosed in a variable temperature oven, and further includes a vaporization block connected to an input end of the chromatographic column. A detector block is close-coupled to the output end of the chromatographic column by a light-tight coupling. The detector block includes a detection chamber which is connected to a fluorescence-producing light source by means of a special fiber-optic bundle, enclosed in a light-tight flexible conduit.
The detection chamber may be monitored by one or two light sensors, more particularly photo multiplier tubes (PMT). One PMT may be used to detect emitted fluorescence of a compound in its gas phase and the other PMT used to detect the amount of fluorescence producing light transmitted by a compound in its gas phase.
The detector block includes a heater element and a temperature sensing element which maintain the temperature of the block at a temperature substantially similar to that of the chromatographic column at the time the first effluents pass from the output end of the chromatographic column into the detector block.
The use of special fiber-optics to transmit flourescence producing light to the detection chamber and to transmit light from the detection chamber to an intensity detector enables the close coupling of the detector block to the chromatographic column and eliminates the need for heated transfer lines between the column and the detection chamber. The flexible light conduit is also a vibration dampener and enables a precise directing of light from the light source into the detector block without the light source being a physical part of the detector block.
These and other advantages and objects of the present invention will become more fully apparent as the description which fillows is read in conjunction with the accompanying drawings.